Nobody laughed two years ago when Jimmy Carter toasted Mexican President Jose Portillo with a small joke about "Montezuma's revenge." And one of the few remaining mysteries of the Carter administration is the identity of the speechwriter who penned that line.

"That shall remain shrouded forever," says Rick Hertzberg, a former Carter speechwriter.

Even the most likely suspect denies it. Harvey Miller, a Los Angeles comedy writer the Carter White House occasionally called for help, emphatically denies he wrote the line, though the White House called him hours before Carter delivered it.

"My phone rang at 6 a.m.," recalls Miller, 45. "I picked it up and heard this crackling noise and a voice asking: 'Harvey Miller?' I thought, Lord, they've dropped the bomb and you're calling to tell me -- how nice."

But it was Hertzberg en route to Mexico aboard Air Force One, calling Miller because the president needed an opening remark to break the ice at his meeting with the Mexican president. As Miller recalls it, he groggily told Hertzberg he couldn't help.

"The next day I read the Montezuma joke," says Miller, "and CBS called to ask if I'd written it. I said later to Rick that I didn't know if I could do this anymore because the president was ruining my reputation."

Miller's association with Washington was a strange marriage between show business and politics. (Hertzberg's dealings with Miller were always by phone -- they've never met.)

"Rick asked if I was a patriot," Miller remembers. "I said, 'I guess there's no money involved.'"

There wasn't, though Miller didn't much need it. He was a successful television and movie wirter who, most recently, was part of the trio that wrote and produced Goldie Hawn's new movie, "Private Benjamin."

During the Carter years Miller turned out as many as 25 jokes at a time. Carter didn't use all the lines. (Sample unused boffola: Shortly after his 1976 election, suggested Miller, Carter should announce he had no grudge against Gerald Ford and, to prove it, he was pardoning Ford.)

Miller says he never knew if his material was funny.

"I'd call Rick's office and his secretary would take the material down and never laugh," he says. "I'd ask, 'Are these funny?' and she'd say, 'I don't know -- I'm busy.'"